The present disclosure relates to audio encoding technologies.
Moving Picture Experts Group (MPEG) audio encoding is an international standard developed by International Organization for Standardization/International Electrotechnical Commission (ISO/IEC) for high-quality and high-efficiency encoding. The MPEG audio encoding method has been standardized in parallel with moving picture encoding within MPEG installed in ISO/IEC SC29/WG11. Such MPEG audio encoding is an encoding standard which emphasizes minimizing the loss of the quality of subjective sound while realizing a high compression rate.
The MPEG audio encoding algorithm is configured to prevent a listener from perceiving quantization noise occurring during an encoding process through various methods. For example, the MPEG audio encoding algorithm can use a psychoacoustic model to maintain a high quality of sound even after encoding by taking into account the human perception characteristic and removing perceptive redundancy. An audio encoder using the psychoacoustic model can reduce the number of codes and realize a high compression rate by omitting pieces of detailed information which are difficult for a human being to perceive at the time of encoding using the acoustic characteristic of a human being who listens to an audio signal.
The audio encoder using the psychoacoustic model uses a threshold in quite, which is a minimum sound level that can be heard by a human being and a masking effect in which sound having a level less than a threshold value is shielded by specific sound. For example, in the audio encoder using the psychoacoustic model, frequency components having a very high or low level, which are rarely heard by a human being, can be excluded from the encoding process, and frequency components shielded by specific frequency components may be encoded with accuracy lower than original accuracy.
The audio encoder using the psychoacoustic model performs quantization and encoding for data using values which are calculated based on the psychoacoustic model. For example, an MPEG audio encoder converts audio data of the time domain into audio data of the frequency domain, finds the amount of maximum allowed noise (that is, maximum allowed distortion) in each frequency band using a psychoacoustic model module, and then performs quantization and encoding based on the amount of maximum allowed noise.